The present invention relates to a torque distribution control system for a four-wheel drive motor vehicle having a central differential.
Japanese Patent Application Laid-Open 62-31529 discloses a system for controlling torque distribution in a four-wheel drive motor vehicle of the rear drive type with a front-mounted engine. The system has a fluid operated clutch as a transfer clutch. A desired torque distribution ratio of torque is calculated in accordance with the difference between speeds of the front-wheel and the rear-wheel. Clutch pressure in the transfer clutch is controlled based on the desired torque distribution ratio so as to prevent the vehicle or the wheels from spinning or drifting.
In ordinary driving, the vehicle is driven through a two-wheel driving system by the rear wheels. When the vehicle is driven on a slippery road, the torque is distributed to the front wheels and controlled for preventing the wheels from spinning. Consequently, such a system can not be employed for the four-wheel drive vehicle which makes a turn with the four-wheel driving system in ordinary driving at an optimum distribution of the torque.